This invention relates, in general, to semiconductor devices, and more particularly, to semiconductor devices used as heaters.
In some semiconductor applications, it is necessary to adjust the resistivity of a resistive element in a circuit to tune the response of the circuit to a particular application. One previously known method for adjusting the resistivity of a material, such as tungsten silicide, forms a heating element under the tungsten silicide. The heating element typically consists of a layer of polysilicon sandwiched between two insulators of silicon dioxide. A current is then passed through the layer of polysilicon which generates heat and anneals the tungsten silicide. The anneal modifies the stoichiometric properties of the tungsten silicide, which in turn reduces the resistivity of the tungsten silicide layer.
One problem with the above mentioned process is that the heating element not only heats the tungsten silicide layer, but everything within a large radius of the heating element. The thermal isolation of silicon dioxide layers or silicon substrates is poor at best. In order to anneal a tungsten silicide layer, temperatures of 500.degree. C. to 1100.degree. C. are required. Due to the thermal loss to the surrounding areas, this previously known heating element limits the composition of structures that can be built in close proximity to the heating element. Also, this method requires significant power consumption to heat both the tungsten silicide layer and the surrounding mass.
The high temperature requirements and thermal energy loss into surrounding areas restricts the placement in a process flow where the annealing process can take place. Most metal interconnect used in the semiconductor industry cannot be heated above 480.degree. C. This limits the use of the heating element to the portion of the process flow that is prior to the deposition of any metal interconnect layers.
The thermal energy loss into surrounding areas also limits how far this technique can be scaled. The shrinking of this previously known heating element is limited by the thermal conductivity of the materials used to form the heater, instead of the photolithographic process used to pattern the previously known heating element. As a result, this process is generally not scaleable since device geometries are ever decreasing.
By now it should be appreciated that it would be advantageous to provide a heating element with improved thermal isolation from neighboring device structures. It would be of further advantage if the heating element requires less power to perform its desired function and is scaleable with decreasing device geometries. It would be of even further advantage if the heating element can be used in other applications such as chemical sensors and thermal ink jet printers.